This invention relates to an improved process for the isomerization of saturated C6 hydrocarbons. More particularly, this invention relates to a two stage process for the isomerization of saturated C6 hydrocarbons.
In the isomerization of saturated C6 hydrocarbons there are two primary reactions of importance. 
Catalysts and processes for isomerizing saturated C6 hydrocarbons are well known by those skilled in the art, and are described in the patent literature, e.g. in U.S. Pat. Nos. 3,054,832, 3,233,001, 3,277,194, 3,974,061, 4,655,484, 4,149,993, and 5,336,692. However, there are ever present incentives for the development of new and/or more effective processes for isomerizing saturated C6 hydrocarbons and for providing flexibility in the process to allow preferential production of one C6 product over another C6 product.
It is an object of this invention to provide a novel process and/or system for isomerizing saturated C6 hydrocarbons.
A further object of this invention is to provide an improved isomerization process and/or system of increased efficiency.
It is yet a further object of this invention to provide a two stage isomerization process and/or system useful for isomerizing methylcyclopentane to cyclohexane and for isomerizing n-hexane to isohexanes.
In accordance with the present invention, a process for isomerizing a hydrocarbon feedstock comprising saturated C6 hydrocarbons is provided including the following steps:
contacting the hydrocarbon feedstock, in the presence of hydrogen, with a first isomerization catalyst composition in a first reaction zone operated under reaction conditions for isomerizing hydrocarbons including a first reaction temperature;
withdrawing from the first reaction zone a first intermediate stream comprising cyclohexane and n-hexane;
separating the first intermediate stream into a first product stream comprising cyclohexane and a second intermediate stream comprising n-hexane;
contacting the second intermediate stream, in the presence of hydrogen, with a second isomerization catalyst composition in a second reaction zone operated under reaction conditions for isomerizing hydrocarbons including a second reaction temperature greater than the first reaction temperature of the first reaction zone; and
withdrawing from the second reaction zone a second product stream comprising isohexane.
The process can further include the steps of:
separating the second product stream into an isohexane product stream comprising isohexane and a first bottoms stream comprising n-hexane, methylcyclopentane and cyclohexane;
separating the first bottoms stream into a n-hexane product stream comprising n-hexane and a second bottoms stream comprising methylcylcopentane and cyclohexane; and
introducing at least a portion of the second bottoms stream into the first reaction zone.
In accordance with another embodiment of the present invention, a system for isomerizing a hydrocarbon feedstock comprising saturated C6 hydrocarbons is provided comprising:
a first isomerization reactor containing a first isomerization catalyst composition;
first conduit means operably related to the first isomerization reactor for introducing the hydrocarbon feedstock into the first isomerization reactor;
second conduit means operably related to the first conduit means for introducing a hydrogen stream into the first isomerization reactor;
third conduit means operably related to the first conduit means for introducing a chloride into the first isomerization reactor;
fourth conduit means operably related to the first isomerization reactor and operably related to a first separator for withdrawing a first intermediate stream comprising cyclohexane and n-hexane from the first isomerization reactor and for introducing the first intermediate stream into the first separator, the first separator providing means for separating the first intermediate stream into a first product stream comprising cyclohexane and a second intermediate stream comprising n-hexane;
fifth conduit means operably related to the first separator for withdrawing the first product stream from the first separator;
sixth conduit means operably related to the first separator and operably related to a second isomerization reactor for withdrawing the second intermediate stream from the first separator and for introducing the second intermediate stream into the second isomerization reactor, the second isomerization reactor containing a second isomerization catalyst composition;
seventh conduit means operably related to the sixth conduit means for introducing a hydrogen stream into the second isomerization reactor;
eighth conduit means operably related to the sixth conduit means for introducing a chloride into the second isomerization reactor; and
ninth conduit means operably related to the second isomerization reactor for withdrawing a second product stream comprising isohexane from the second isomerization reactor.
The ninth conduit means can also be operably related to a second separator for introducing the second product stream into the second separator, the second separator providing means for separating the second product stream into an isohexane product stream comprising isohexane and a first bottoms stream comprising n-hexane, methylcyclopentane and cyclohexane; and the system can further include:
tenth conduit means operably related to the second separator for withdrawing the isohexane product stream from the second separator;
eleventh conduit means operably related to the second separator and operably related to a third separator for withdrawing the first bottoms stream from the second separator and for introducing the first bottoms stream into the third separator, the third separator providing means for separating the first bottoms stream into a n-hexane product stream comprising n-hexane and a second bottoms stream comprising methylcyclopentane and cyclohexane;
twelfth conduit means operably related to the third separator for withdrawing the n-hexane product stream from the third separator;
thirteenth conduit means operably related to the third separator for withdrawing the second bottoms stream from the third separator; and
fourteenth conduit means operably related to the thirteenth conduit means and operably related to the first isomerization reactor for recycling at least a portion of the second bottoms stream to the first isomerization reactor.
Other objects and advantages will become apparent from the detailed description and the appended claims.